This project is intended to find and characterize naturally occurring inhibitors of kinins. The assay used in detection and purification is the inhibition of binding of labeled kinin to receptors. The labeled kinin is 125I-tyrosine1-kallidin, and the receptors are prepared from pregnant bovine myometrium. The source of inhibitors is bovine tissue extracts. The first extract being explored is kidney cortex treated with methyl ethyl ketone. Column chromatography of the simple lipids on a lipophilic Sephadex has shown the existence of four or more substances that can inhibit receptor binding of bradykinin. Purification, chemical characterization, and tests of these inhibitors in living target tissues is in progress.